Advancement of Intensity Duration Frequency (IDF) Curve Through Possible Probability Distribution Method Using Disaggregated Precipitation Data; The Case of Wolkite, Ethiopia

Rainfall is one of the key inputs for surface water resources and groundwater recharges. This rainfall is recorded in depth format (mm or in) using a rain gauge in the gauging station. Some models need this rainfall record in intensity format (example, mm/hr or in/hr). In addition, design discharge, especially flood-related structures, requires extreme rainfall intensity values. In Ethiopia availability of on hand rainfall intensity data in shortest duration is in scarce and the same for the selected area called Wolkite. Therefore, this study aims in developing Intensity Duration Frequency curve through probability distribution methods using disaggregated data that fits the study area. For this purpose, six distribution methods, namely, general extreme value I, Gumbel, normal, log-normal, Pearson, and log-Pearson were examined based on different comparison criteria. Normal distribution method found to be the best method that fits the data applied and Intensity duration curve was developed using this method. Finally, the developed Intensity Duration Frequency curve was calibrated and evaluated with Non-Probability Intensity Duration Frequency Models and results a Performance indicator value of Coefficient of determination (R²), Nash-Sutcliffe efficiency (NSE) and Percent bias (PBIAS) of 0.96, 0.964, and -6.35% which are in acceptable ranges. Therefore, the derived Intensity Duration Frequency values were possible to apply in developments of any urban and water related structure for required duration specifically in Wolkite town. Also, the research is applied as a guideline in areas where availability of rainfall intensities of shortest duration is in scarce.